Rigify Error Bone cannot connect chain bone
If you move (separate) the spine.004 bone the error appears.
The bone spine.003 and spine.004 have to be perfectly aligned.

Steps (in edit mode):

1.- Selected bone spine.003


2.- MAY+S - Cursor to selected


3.- Select Spine.004 and  selection to cursor


4.- There is no more error and the rig is ok.


I hope I've helped.
R.